Magnetic resonance imaging (MRI), by offering the sole means of imaging human brain structure and activity with high spatial resolution, has evolved into an indispensable tool for studying brain function in health and disease. It is uniquely suited to examining the neural basis of higher order behaviors and cognition, as well as neurodegenerative and developmental disorders, for which animal models are of limited applicability. Yet, because of current experimental limitations, there is wide range of subjects and human behaviors that are completely inaccessible by MRI techniques. MRI currently depends on large, expensive, and fixed scanners in which subjects must remain motionless for long periods of time within a confined horizontal space. Thus any behavior involving motion, and especially those involving the upright real-time interaction with objects in natural environments, cannot be studied. Such studies are of enormous scientific interest, for example, in understanding the neuronal basis of motor planning, but also of considerable practical and clinical importance in order to eventually understand and address the motor deficits associated with injury, stroke, or disease which preclude everyday behaviors as important as feeding and reaching. Of particular relevance in this regard is the large population of people with limited ambulatory or vestibular function or difficulty in maintaining posture or smooth movements for which the requirements of remaining motionless in a horizontal space preclude MRI. There is thus an urgent need for a brain imaging technology that is more portable and less restricting than current MRI scanners. One way to address these issues is to decrease the size of the MRI magnet to make a head-only system which does not confine the body, but this approach leads to drastically reduced static field (B0) homogeneity which, with current technologies, precludes high resolution imaging. Now, with the support from BRAIN Initiative grant R24 MH105998, we have addressed the problem by developing new hardware, as well as new acquisition and reconstruction methods, capable of producing high quality brain images despite extreme B0 inhomogeneity. The goal of this U01 project is to build upon these efforts by designing, building, and validating the first-ever human MRI scanner requiring only the head to be inside the magnet bore and having a large window for viewing outside the magnet bore. The small size, weight, and power requirements of this 1.5 Tesla MRI system will enable it to be transported and sited almost anywhere in the world and will be able to bring the magnet to the subject rather than the other way around. To achieve this, a team of leading experts from multiple disciplines and institutions has been assembled. The hardware and software components of this revolutionary MRI system will be constructed and debugged in the first 2 years of the project, the system will be assembled and tested in years 3- 4, and finally in year 5, the MRI system will be piloted in a first of its kind study of motor coordination and planning during natural reaching behaviors.